1. Field of the Invention
The present invention relates to a device for adjusting the characteristic of a microphone. More specifically, the invention relates to a device that can adjust a transmission sensitivity-vs.-frequency characteristic by an easy operation according to a communication state and a noise environment, thereby invariably ensuring good communication quality.
2. Description of the Related Art
As a traditional method of adjusting the transmission sensitivity-vs.-frequency characteristic of a microphone, it is common practice to employ an additional electronic circuit such as a microphone equalizer. As a method of acoustically adjusting the transmission sensitivity-vs.-frequency characteristic by the main unit of the microphone, a housing that contains microphone elements is drilled in advance, and a resulting opening is covered with a thin piece of Japanese paper or a cloth.
Specifically, in the case of a dynamic microphone, a magnet, a magnetic circuit, and a damping material are provided at the back of a diaphragm in the microphone. Then, by means of a hollow, cylindrical housing with its back surface sealed, a space that contains these members is formed. In addition, an opening is formed in the peripheral wall portion or the back surface of the housing. Then, by sealing the opening with a piece of Japanese paper or a cloth, it is arranged such that an appropriate pressure is applied to the back surface of the diaphragm that vibrates by a sound pressure.
If the space behind the diaphragm is completely sealed, a response at low frequencies deteriorates. On the contrary, if the above-mentioned method is employed, acoustic low-frequency compensation becomes possible because the piece of Japanese paper or the cloth functions as a certain acoustic resistive element. Thus, in most cases, the quality of communication that is easily audible can be thereby obtained.
The method of performing the low-frequency compensation like the one described above is adopted in various forms in telephones and headphones.
The method of acoustically adjusting the transmission sensitivity-vs.-frequency characteristic by means of the microphone main unit has the advantage of preventing distortion and deterioration in an SN ratio, compared with the method of electrically adjusting the transmission sensitivity-vs.-frequency characteristic by means of the microphone equalizer circuit. However, in regard to the method described above, the following problems are pointed out.
First, generally, if the transmission sensitivity-vs.-frequency characteristic is flat in an audio-frequency band, it is said that good communication quality can be obtained. However, in radio communication apparatuses such as amateur radio communication apparatuses, an audio signal that is easily audible is not always obtained in normal conditions as described above. Thus, the communication quality varies according to a communication state and a noise environment.
Accordingly, in order to ensure good communication quality, it is not enough to perform uniform low-frequency compensation alone, as seen in the above-mentioned conventional art, so that means for allowing adjustment to and setting the characteristic is required.
Further, upon reception of a notification that an audio output reception state is not satisfactory during communication, the radio communication apparatus should address this state immediately. However, the causes of this state are diverse, so that even if a receiving side makes micro adjustment to the communication frequency bands such as using a WIDTH function or a SHIFT function in the communication apparatus, this state cannot always be improved. Even a skilled operator is bothered by the operation of addressing this state.
The present invention therefore has been made with the object of providing a microphone having a configuration that can adjust the transmission sensitivity-vs.-frequency characteristic by an easy operation. According to the present invention, just by performing a quick operation on the microphone, good communication quality can be ensured in a radio communication apparatus.
The present invention relates to a microphone characteristic adjustment device, which comprises a microphone main unit that contains microphone elements in a hollow, cylindrical housing with its back surface sealed. The housing includes a diaphragm disposed on its front side and openings are formed in the peripheral wall portion of the housing, for communicating a space formed behind the diaphragm with the outside of the housing. The microphone characteristic adjustment device further comprises packing formed of an elastic member, being fitted over or wound around the periphery of the microphone main unit for securing. Openings are formed in the packing at locations corresponding to the positions of the openings in the housing of the microphone main unit. The microphone characteristic adjustment device still further comprises an adjustment ring, having a hollow, cylindrical shape to be fitted over the periphery of the packing, for rotating around the periphery of the packing while keeping in contact with the periphery of the packing to form a ventilation path for setting one of the openings in the packing to be communicated with the outside or not to be communicated.
According to the present invention, the space formed behind the diaphragm in the microphone main unit is communicated with the outside through the openings formed in the housing, the openings in the packing, and the ventilation path in the adjustment ring. Then, by rotating the adjustment ring, the communication state and the noncommunication state can be set. In other words, whether low-frequency compensation in the transmission sensitivity-vs.-frequency characteristic should be provided or not can be selectively set.
Further, if the openings in the microphone main unit, the openings in the packing, and the ventilation path in the adjustment ring are formed to be elongated in the periphery direction, the cross-sectional area of a communication path can be gradually changed according to the rotation angle of the adjustment ring. The transmission sensitivity-vs.-frequency characteristic can be thereby changed smoothly.
Further, if the width of the elongated openings in the packing is varied along the periphery direction, the above-mentioned characteristic with respect to rotation of the adjustment ring can also be changed nonlinearly.
Since the elastic member is employed for the packing, the adjustment ring is fitted over the packing, insuring an appropriate fit. The adjustment ring is thereby rotated around the packing, while keeping in contact with the packing. Due to this appropriate frictional relationship, an adjustment operation is facilitated. In addition, even if the microphone undergoes vibration, the problem of sound absorption resulting from rattling of the adjustment ring can be prevented. In addition to rubber, resins such as felt can also be employed as a material for the packing.